Well, I state that I don't understood very well how Install them, so maybe the mistakes are all mine, but I need your help so I hope to shed light on these my gaps .

I grab the BMW Isetta mod just for make a try. I use XTractor extracting Sounds & models, then I copied and pasted all inside those files, Sounds with sounds,models with models,maps with maps and etc..
I run Mafia and the mod doesn't absolutely work..

Where did I go wrong? I should had the 1.2 version of the game (although it still says that it is version 1.0). The same things with the Widescreen fix.

When installing any mod be it a change in the gameplay
or the use of cars, widescreen etc. You only need to
patch the rw_data.dll with Data Xtractor there is no
need to extract any of the data; the folders from the
mods are sufficient.

The actual version of the game is not found by right-clicking game.exe
and then properties/details. To check what version you need to go
into regedit then HKLM/Software/Wow6432 Node/Illusion Softworks/Mafia
If the game is installed as it should be you should find what version you
have.